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Sunday, November 29, 2009

Cassini's surprise discovery of active plumes on Enceladus has made that moon a priority target for future exploration. The key question is whether their is an internal ocean that might -- like an internal ocean might within Europa -- harbor life. Even if Enceladus turns out to be lifeless, the existence of the plumes provides an inexpensive opportunity to sample the interior of an ice world.

Two Decadal Survey White Papers address science goals for future Enceladus exploration. The first, The Case for Enceladus Science, lays out the key scientific questions that future missions would address. If the Saturn Titan System flagship mission (~$3B) eventually flies, these questions will guide the planning of its Enceladus encounters. However, a flagship mission will not arrive at Saturn for at least another 15 to 20 years. Several of the authors of the science paper contributed a second paper, The Case for an Enceladus New Frontiers Mission to propose a mission that might launch in the coming decade. (New Frontier missions cost ~$650M.)

This mission would use solar power and batteries to avoid the costs of a plutonium power supply. Just four instruments would be flown:

"Mid-IR Thermal Instrument (MIRTI): The mid-infrared thermal mapper measures temperatures in the vent region, and can search for other regions on Enceladus that may be warmer than their surrounding areas. [This instrument would have both finer spatial and spectral resolution than Cassini]

"Ice Penetrating Radar (IPR): An ice penetrating radar system provides the best single measurement to determine Enceladus’ sub-surface structure, and unlike direct seismometry, does not involve touching the surface with its implications for planetary protection. [Cassini lacks this instrument]

"Enceladus Mass Spectrometer (EMS): Thus, to study all biologically interesting amino acids, while also studying bulk composition and high-order hydrocarbons, requires a mass range up to a minimum of 300 Daltons, with a mass resolution (m/Dm) sufficient to resolve molecular isotopes (m/Dm of 500). [Cassini's mass spectrometer measures only to 100 Daltons; a Dalton is another term for an atomic mass unit.]

"Imaging camera for Enceladus (ICE): The imager is a multi-spectral camera, capable of pushbroom imaging and high spatial resolution (5 m) to resolve the polar vents and other surface structures. [Resolution would be as fine as 5 meters.]

"Gravity Experiment: While not strictly a science instrument per se, it is highly desirable to further refine our knowledge of the Enceladus gravity field by performing multiple gravity passes. Passes at different sub-spacecraft latitudes will help constrain the interior structure."

The White Paper goes on to specify a number of mission requirements to fulfill the science goals. For example, the Enceladus Observer (to give this mission a name) would need at least 12 enounters at 100 - 200 kim altitude at various latititudes including both poles and the equator to determine core size and crust thickness. Pointing accuracy of the cameras would need to be 2 mrads to accomplish the imaging goals. Several flights through the plumes would be required.

After a 9.4 year flight to Saturn, the mission begins with four Titan encounters that set up the Enceladus encounters, which would typically occur at 4 km per second every 6.85 days.
Editorial Thoughts: I suspect that many of the readers of this blog imagine missions they would like to see fly. I'm no exception, and this is a mission I would like to see fly -- with a few modest enhancements. First, I'd like to see a near IR imager added that would be optimized to image Titan's surface through the spectral windows in it's clouds. And second, I would enhance the mission's satellite tour.

For the latter, I would include more Titan enounters to study its surface and upper atmosphere. (The White Paper states, "Titan science could also be accomplished with a spacecraft studying Enceladus, during many Titan flybys.") Then there would be a series of Enceladus encounters to fulfill the core Enceladus science much like those outlined in the White Paper. An extended mission could significantly enhance the science return. New astrodynamics studies have found that two years of encounters with Rhea, Dione, and Tethys would lower the Enceladus encounter speeds to ~1 km per second for around 50 encounters per year. Encounters with the other moons of Titan with this instrument set would allow comparative studies among the medium sized moons of Saturn. It's possible that the mission could end with the spacecraft entering orbit around Enceladus, again thanks to astrodynamic methods developed in the last few years.

And while I'm day dreaming, I'd like to see the mission enhanced to the small Flagship class (~$1B) by carrying a Titan lake lander that might be supplied by ESA. While I understand why Jupiter-Europa were prioritized over Saturn-Titan-Enceladus for the coming decade (technology readiness), I would like to see both an observer-class orbiter and a lake lander fly in the next decade. Twenty years is too long too wait.

Costs from the mission presentation. 2006 costs were those from a 2006 Mars Scout proposal that were judged to be too low

As with many missions, there are some unique aspects to this mission. First, there are two nearly identical spacecraft, so there are dollars for extra parts purchases. However, the nearly identical designs allows the design and testing dollars to be shared across both spacecraft. I've read that the cost of a second nearly identical craft is around an additional 60%. (Sometimes I've seen lower figures, but those seem to be for missions that have hot, flight ready spares so duplicate systems and even entire craft are already figured into the base mission costs.)

The MACO mission proposed to fly just three instruments, resulting in fairly low instrument costs. (I've seen estimates for individual instruments easily top the figure for this mission.) This mission also has relatively low data rates and moderate pointing costs. If a high resolution camera were to be added, costs would likely increase significantly to provide the spacecraft stability and aiming to point the camera accurately. A more capable data storage and communications system would be needed to handle the much larger data stream.

A team has proposed a clever new way to measure the physical properties and composition of the Martian atmosphere with high resolution. The approach could significantly enhance the proposed Trace Gas Orbiter mission.

Goals for the study of Mars' atmosphere

Studies of the Martian atmosphere have remained a high priority for a number of reasons: To provide a comparison to our own planet's climate and weather, as a record of the evolution of Mars, as evidence of current biological or geological activity, and to understand the conditions that probes will encounter during their entry and descent to the surface.

Satellite studies of the Martian atmosphere traditionally have used spectrometers, radiometers, and radio tracking to measure the atmosphere. All are time tested methods. The first two are used by satellites to measure temperature and composition for our own atmosphere. The last method has been used widely at planets with atmospheres (even with atmospheres so thin that they are almost vacuums) and use shifts in radio transmissions from the spacecraft received at Earth to measure values such as pressure and temperature. All three methods have their limitations. Spectrometers and radiometers integrate data from large volumes, and hence lack spatial precision. Radio tracking is limited to locations where the spacecraft's orbit or trajectory carry it behind the atmosphere and don't use optimum frequencies for atmospheric studies.

A team led by E.Robert Kursinski of the University of Arizona has proposed a Mars mission that cleverly addresses a number of key measurements. Called the Mars Astrobiology and Climate Observatory (MACO), the mission would send to orbiters to Mars. The satellites would use spectrometers and radiometers for traditional atmospheric studies much like the proposed Trace Gas Orbiter would to measure atmospheric structure and composition. The clever part is that the spacecraft would transmit a milimeter wave signal to each other in a manner reminiscent of radio tracking. The choice of millimeter wavelengths, however, makes it a much more sensitive probe of the atmosphere for key trace gases than are the frequencies used for radio tracking.

The orbits of the two craft would be chosen to enable approximately 30,000, globally distributed profiles of the atmosphere per year. The quality of the data from each profile would be similar to that which a dedicated atmospheric entry probe might gather. For example, measurements of near surface conditions would be accurate to approximately 100 meter strata. Spectrometers and radiometers, by comparison, measure values for strata an order of magnitude or two larger. These satellite-to-satellite techniques are beginning to be used for satellite to satellite Earth measurements, so the theory is sound and the research community has experience with the techniques.

MACO was proposed for the 2006 Scout mission selection. It received the highest science rankings, but the reviewers believed that it was unlikely to be implemented within the budget. The team is now educating the Decadal Survey on the science and implementation options in the hopes that it will receive a high priority. A new variant of the mission is also being studied. The original proposal had two highly capable spacecraft. The new variant would have a primarly spacecraft and a small sub-satellite that would transmite the millimeter wave signal to the main spacecraft.

Editorial Thoughts: The improvement in measurement precision (both of trace gas abundances and spatial resolution) appear to me to be quite significant. (Full disclosure: I'm not an atmospheric remote sensing scientist.) If the claims are solid, then I think that the proposed 2016 Trace Gas Orbiter mission would be significantly enhanced at a relatively minor cost by adding the sub-satellite. I think this is a clever proposal and hope it will be seriously evaluated by the Decadal Survey.

Thursday, November 19, 2009

The ESA/JAXA BepiColombo mission that once faced possible cancellation because of budget overruns, has been approved for development (at the higher costs) to eventually reach Mercury orbit in 2020. The BBC has an article on the (Mercury mission clears key hurdle) approval. As the article states,

"Dr David Rothery, the lead scientist on Bepi's Mercury Imaging X-ray Spectrometer (MIXS), said the science case for another Mercury mission was exceptional.

'The best way I heard it expressed, very kindly by a member of the Messenger team, was that Messenger is providing the 'hors d'oeuvre' and BepiColombo will be the 'feast'.

'BepiColombo has more instruments and more capable instruments than Messenger does."

I have also reposted the blog entry on why a comet sample return mission is so hard. I normally clip the images from presentation on my workstation, but that machine has been tied down doing multi-day data analyses. For the original post, I clipped the images on my netbook. Lesson learned, clip from a big screen.

Bruce Moomaw has also been digging into the history of presentations on this topic and has some corrections and extensions to my post:

I had written: "The small body science community has ranked a comet sample return as its top priority for the last decade or so. This mission was included (optimistically, for reasons explained below) in the first set of mission candidates for the New Frontiers (~$650M) missions and remains on that list."

Bruce corrects my poor memory: "Actually, the comet sample return included in the first set of NF mission candidates (as listed in the previous Decadal Survey) was the less ambitious warmer Comet Surface Sample Return, rather than the Comet Cryogenic Sample Return, which was recognized in the first Survey as a mission sufficiently difficult that it was Flagship class. And it's the Comet Surface Sample Return that was listed among the acceptable candidates in the first New Frontiers solicitation. The considerably greater difficulty of the CCSR has been clearly recognized from the start."

"Note also the very next page in the CNSR (aka CCSR) presentation that you quote: "If you can’t maintain cold enough temperatures to preserve the ice sample during return, then at least collect the evolved gases. Must also store them in a way that prevents chemical changes (e.g., using special getters, different chambers filled at different temperatures)." The Small Body scientific community seems to regard this as a clearly justifiable mission, although of course they'd prefer a cryogenic return if there was the money for it.

" I do note from Hal Weaver's and Michael A'Hearn's Nov. 2007 advance report that CSSR would use "flasks" (in the plural) to collect those gases, which presumably is the same thing Weaver mentioned in his new CNSR presentation. Note also from the 2007 mission presentation (pg. 17) that only one out of 11 SDT members thought volatile preservation in flasks was an absolute necessity for the mission, although the others considered it "highly desirable" and it is baselined."

I still think that this is a very complicated mission given the sampling challenges and the necessity to preserve the evolved gases. I hope that the community comes up with good solutions to the problem. I want to see this mission fly.

I really appreciate corrections. Planetary exploration is a huge field, and I follow it part time as a hobby while (supposedly) writing my dissertation in an unrelated field. Please point out my errors and omissions!

Wednesday, November 18, 2009

A number of news reports suggest that the U.S. administration will ask non-entitlement* and non-defense budgets to take a 5-10% budget cut in the Fiscal Year 2011 budget. A budget cut at the high end of that range carried out over a decade would eliminate a mission roughly the size of a New Frontiers mission. Additional budget cuts in future years would also be possible.

Currently, NASA's projected budgets (from the FY10 budget package) would provide approximately $12B over a decade to develop planetary missions (http://futureplanets.blogspot.com/2009/09/thoughts-on-scary-messages.html). There has been talk that NASA would receive an increase next year to put the manned spaceflight program back on track. Also, there are long term promises to increase spending on science programs of all types. Given the competing pressures, several scenarios could play out; for example:

All NASA programs receive budget increases

The manned portion of NASA's budget receives an increase but the science program remains flat at best or is cut

All NASA programs receive budget cuts

Editorial Thoughts: Whatever happens to NASA's budget next year, the political pressure to reduce deficits seems strong in both parties. We may see multiple cuts to the planetary program over the coming decade. Given this, in my opinion, a key measure of the success of the Decadal Survey is to propose a prioritized set of missions that remains robust even in the face of declining budgets (and likely cost overruns on some early missions in the queue). It is quite possible that the lower priority missions will never fly because of insufficient funds. An interesting question is whether the Survey will prioritize smaller missions (support a diversity of targets) or larger missions (in-depth study of one to two targets) as higher priorities.

*Budget Primer: I find the budgeting processes of other nations confusing and suspect that many of this blog's readers may find the U.S. process confusing. There are four large pots of spending in the U.S. budget: Entitlements (social security and medical funding for retirees, etc.) at 54%, payment of interest on the national debt 8%, military spending 21%, and everything else 17%. (Breakdown from FY08 from http://en.wikipedia.org/wiki/United_States_federal_budget) Interest spending cannot be avoided, and it is politically challenging to cut entitlements and military spending. Therefore, attempts to reduce deficit spending tend to fall on the everything else category that includes NASA, the FBI, national parks, and many other functions.

Sunday, November 15, 2009

The small body science community has ranked a comet sample return as its top priority for the last decade or so. This mission was included (optimistically, for reasons explained below) in the first set of mission candidates for the New Frontiers (~$650M) missions and remains on that list. In the current Decadal Survey, the goal of the community appears to secure funding for serious technology development to enable fhe mission for the following decade.

A recent presentation to the Decadal Survey Small Bodies panel (http://www.spacepolicyonline.com/pages/images/stories/PSDS%20PB2%20Weaver.pdf) illustrates why this mission is so hard. The first requirement, to keep the ices collected frozen, may be the hardest. It is the ices and their record of the early solar system's volatile inventory that makes this mission so valuable. The samples, however, have to be kept frozen during the collection, then within the sample return capsule for the long flight home, during the atmospheric entry, and finally during the capsule retrieval.

(The freezing temperature of water at sea level is 273 K).

Another challenge is design the mechanism(s) that will collect the sample from potentially meters inside the comet. A recent examination of technology obsticals for sampling near Earth asteroids (http://futureplanets.blogspot.com/2009/10/parting-look-at-primitive-body-sample.html) put it bluntly: it is not clear how to design a reliable sampling mechanism for near Earth asteroids. This is probably even more true when your goal is not to sample the surface of a rocky asteroid, but to sample at depth a mixture of ice and rock.

A third challenge is that we know little about the surface of comets. We know only that they exhibit a wide range of geomorphologies. Whether that diversity extends a variety of surface and near surface types at the scale at which a lander would sample is unknown. This simply makes designing the sampling mechanism that much harder. The Rosetta mission's lander will tell us a great deal about the surface of one comet, but even if we can rely on its data for all comets, the answers could not be incorporated into a mission that would fly before the end of the coming decade at the earliest.

It now seems to be generally accepted that returning a frozen sample of a comet is beyond the scope of a New Frontiers class mission and is probably is a $1-2B mission. In recognition of this, NASA is now willing to allow a mission that returns a dust sample plus the thawed remains of any volatiles:

"Scientific community interest in a Comet Surface Sample Return (CSSR) mission has been very high for many years. The advantages of such a mission have been stated in many documents including the decadal survey. Flyby missions to comets are fairly simple, and the Deep Space-1, Stardust, and Deep Impact missions have produced remarkable data. Rendezvous missions such as the ESA’s Rosetta mission (Figure 2.3) are more challenging, and a sample return mission can take twice as long as a rendezvous mission, thereby increasing cost and risk. The decadal survey concluded that bringing back a warm (i.e., non-cryogenic) sample was within a New Frontiers mission budget. While cometary science goals make the return of a cryogenic core sample highly desirable, such a mission may not fit within the fiscal limits and programmatic timescale of the New Frontiers Program. The science yield from a warm sample return mission will have to be strongly defended by proposers."

After my previous post on Saturn atmospheric probes, Bruce Moomaw pointed me to a 2007 presentation (http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/41220/1/07-1820.pdf) that had much more information on trajectories for the Saturn encounter. In this study, two probes would descend to 10 bars (a shallow depth) for in situ studies while the carrier craft would probe the atmosphere to 100 bar depths with a microwave radiometer. The latter measurements can only be made from within 60,000 km. A flyby carrier can easily get close enough with a periapsis of 11,700 km. An orbiter would come only within 60,000 km on it's initial trajectory. Subsequent orbits, such as those planned for the Cassini end of mission, would have to be used to get close enough for effective radiometer measurements.

Friday, November 13, 2009

A key goal of planetary science has been to understand the formation, evolution, and internal structure of the gas giants. Galileo and Cassini have studied the outer skin of Jupiter and Saturn, but the data returned has not provided answers to key questions on these issues. The Galileo atmospheric probe was intended to address many of the compositional questions (which relate to key questions of formation and evolution), but it was skunked by entering in a hot spot that both lacked clouds and water vapor.

In the last few years, plans have been made to address these questions with new and extended missions. The Juno orbiter to Jupiter will address all three questions by probing the composition and structure of the atmosphere and will study the deep interior through precise gravity and magnetic measurements. Its close orbit -- cloud skimming on the scale of the Jovian system -- enables these studies. The final stages of the extended Cassini mission will bring it equally close to Saturn for precise gravity and magnetic measurements. (Alas, Cassini lacks Juno's microwave radiometer for deep probing of the atmospheric structure and composition.)

Juno and Cassini will not be able to address all the key composition questions. Those lines of inquiry require the precise measurements that can only be made from within the atmosphere. This is considered so important that the original concept for what became Juno had both the orbiter and new atmospheric probes for Jupiter. Unfortunately, the technology to build and test heat shields for the extreme heating encountered in a Jupiter entry has been lost.

Fortunately, the challenges for entering Saturn's atmosphere are much less severe, and scientists are proposing an atmospheric entry mission for that planet. While Saturn is not identical to Jupiter, it is similar enough that measurements made there will answer questions relevant to both planets. (Even if new Jovian probes were programmatically possible, scientists would want probes for Saturn to compare the two worlds.)

Two presentations at a recent Outer Planets Panel for the Decadal Survey addressed the science rational and possible approaches for a Saturn probe mission. A fundamental challenge of the mission is that reaching the depths where water vapor will be present (a key measurement) requires operation to depths of 50 - 100 bars. (A bar is the pressure of Earth's atmosphere at sea level.) Not only does this require a sturdy pressure shell, it is difficult to maintain adequate communication rates with a relay spacecraft, and the battery would have to be large to provide power for an extended descent.

Several solutions to the problem of studying the deep atmosphere were proposed:

Have the probe piggyback a microwave radiometer that would measure water abundances prior to entry from just above the atmosphere as Juno will do for Jupiter. The radiometer would be jettisoned just before entry. Alternatively, the carrier craft could carry the radiometer, although that would require a flyby or orbit that passes just above the atmosphere.

Have a two stage probe where the larger, more instrument laden probe falls slowly on a parachute while a smaller probe with just an instrument or two falls quickly to the necessary depth

Forgo the deep measurements and focus on multiple shallow probes to study several locations in Saturn's atmosphere

While no cost estimates were provided, one of the presentations states that a probe mission "may exceed" the cost of a New Frontiers (~$650M) mission and recommends a new class of $1.2-1.5B missions. (This sounds like a strong hint that a probe mission is likely to be closer to $1B than $650M).

Editorial Thoughts: In-depth (literally) exploration of the gas planets likely will be a continuing priority for decades. After Juno, the Cassini end of mission, and an eventual probe mission to Saturn, the science community is prioritizing missions in the same class to Uranus and Neptune.

In theory, a Saturn probe does not require a dedicated mission. Any spacecraft traveling to or passing by Saturn could drop off a probe. It's possible that Saturn may be a busy place in the coming decade with the proposed Argo mission passing through on its way to Neptune and the Kuiper belt, a possible Titan lake lander, and a small orbiter to continue the exploration of Enceladus and possibly Titan. Celestial mechanics may make piggy backing difficult in some of these cases. The Argo craft, for example, would need to thread a narrow path to get the gravity boost, and that path may not allow a probe delivery and relay. Even if celestial mechanics cooperate, carrying the extra weight of the probe and the communications relay equipment will add costs to a mission.

I personally would like to see ~$2B budget to continue the exploration of the Saturn system in the coming decade with a Titan lake lander, a small orbiter, and an atmospheric probe or two (in that order of priority). With approximately $7B of the coming decade's expected $12B budget for planetary missions, committing these funds would mean many other planetary targets would not be explored. (I'd also like to see $2B dedicated to Venus studies and $1B or so to small bodies studies...) It will be interesting to see where Saturn falls in the Decadal Survey's priorities.

Resources

Presentations to the Outer Planets panel (images in this post taken from the first presentation)

ESA is expected to provide a billion euros (~$1.4-1.5B depending on currency fluctuations). No mention is made of NASA's contribution, but based on current budget projections, NASA is likely to contribute several billions of dollars.

The planned missions are as described previously in several blog entries:

2016 - ESA provided orbiter with NASA launch to study trace gases. ESA will also provide a lander that will demonstrate landing technology and carry a weather station. No mention of how long the instruments are expected to function.

2018 - ESA and NASA rovers carried to the same location by NASA's skycrane landing system.

2020 - A network mission is under consideration.

Editorial Thoughts: This would seem to lock in the 2016 and 2018 into NASA's plans for the next decade. The Decadal Survey in progress is specifically limited to proposing missions beyond currently committed missions. By the time of the 2012 Decadal proposal a number of missions are likely to be in that category: the 2016 and 2018 joint Mars missions, the Jupiter Europa Orbiter,a to be selected New Frontiers, and a to be selected Discovery mission. (I'm probabably missing a mission or two. I haven't included missions expected to launch by or within a year or so of the report.) The actual budget left for the Decadal Survey to work with may be fairly small. By my rough accounting, the list above could be in the neighborhood of $7B (before cost overruns) out of an expected decadal $12B.

Saturday, November 7, 2009

Science@NASA has a nice article on the motivation behind the 2013 MAVEN mission to study Mars' atmosphere. To whet your appetite, here are a couple of quotes:

"Nov. 6, 2009: Once upon a time — roughly four billion years ago — Mars was warm and wet, much like Earth. Liquid water flowed on the Martian surface in long rivers that emptied into shallow seas. A thick atmosphere blanketed the planet and kept it warm. Living microbes might have even arisen, some scientists believe, starting Mars down the path toward becoming a second life-filled planet next door to our own.But that's not how things turned out."

"One way or another, scientists believe, Mars must have lost its most precious asset: its thick atmosphere of carbon dioxide. CO2 in Mars's atmosphere is a greenhouse gas, just as it is in our own atmosphere. A thick blanket of CO2 and other greenhouse gases would have provided the warmer temperatures and greater atmospheric pressure required to keep liquid water from freezing solid or boiling away."

"MAVEN will be the first mission to Mars specifically designed to help scientists understand the ongoing escape of CO2 and other gases into space. The probe will orbit Mars for at least one Earth-year. At the elliptical orbit's low point, MAVEN will be 125 km above the surface; its high point will take it more than 6000 km out into space. This wide range of altitudes will enable MAVEN to sample Mars's atmosphere more thoroughly than ever before."

Editorial Thoughts: A lot of science doesn't involve flashy exploration or engaging images. MAVEN and the Lunar GRAIL missions are solid examples of the planetary missions that collect data that tell important stories only after careful analysis. As the easy missions to many destinations are completed, these are the yeomen missions that will fill in important gaps in our understanding of processes. [Note: A previous version of this entry mentioned a lunar GRACE mission when I meant to say GRAIL mission. They are similar missions, but the former studies the gravity field of the Earth and the latter will do the same for the moon.]

The principle investigator, Dr. Sharpton, sent me the following synopsis of the mission: "RAVEN, utilizes the latest in the RADARSAT lineage, extending back to 1996 (RADARSAT 1 launched in Nov. '95). We can accomplish reconnaissance level mapping of Venus at 30-m/px and map about 25% of Venus each cycle (a venusian day). Alternatively, we could map about 3% of the planet at 3-m resolution each cycle. Obviously, we would want to have a combination of resolution modes and have overlap so that we can extract topography. Topographic resolutions would be on the order of 20m vertical resolution and either 300-m postings (if using 30-m images) or 30-m postings (with 3-m images). If InSAR turns out to be feasible (we believe it will), the vertical resolutions would drop to a meter or less."

Dr. Sharpton pointed me to an AGU abstract about the mission. Since there is no easy way to link to AGU abstracts, I'm posting parts of it below. You can search for it and other planetary abstracts athttp://agu-fm09.abstractcentral.com/planner

It has been more than 15 years since the Magellan mission mapped Venus with S-band synthetic aperture radar (SAR) images at ~100-m resolution. Advances in radar technology are such that current Earth-orbiting SAR instruments are capable of providing images at meter-scale resolution. RAVEN (RAdar at VENus) is a mission concept that utilizes the instrument developed for the RADARSAT Constellation Mission (RCM) to map Venus in an economical, highly capable, and reliable way. RCM relies on a C-band SAR that can be tuned to generate images at a wide variety of resolutions and swath widths, ranging from ScanSAR mode (broad swaths at 30-m resolution) to strip-map mode (resolutions as fine as 3 m), as well as a spotlight mode that can image patches at 1-m resolution. In particular, the high-resolution modes allow the landing sites of previous missions to be pinpointed and characterized... Our current estimates indicate that within an imaging cycle of one Venus day we can image 20-30 percent of the planet at 20–30-m resolution and several percent at 3-5 m resolution. These figures compare favorably to the coverage provided by recent imaging systems orbiting Mars. Our strategy calls for the first cycle of coverage to be devoted to imaging large geographic areas (e.g., Thetis Regio) at 20–30-m resolution with interleaved observation of pre-selected targets at high resolution. The second cycle will include additional imaging, but the focus will be repeat-pass coverage to obtain topography for a significant fraction of the first-cycle targets... All components of the spacecraft are expected to remain operational well beyond the nominal mission time, so global mapping at 10 m or better resolution during an extended mission is conceivable."

Sunday, November 1, 2009

A major criticism of both the last astronomy and the last planetary Decadal Surveys was that they prioritized ill-defined mission concepts whose true cost was severely under estimated. As a result, both fields have had embarrassingly large cost overruns on key projects -- the James Webb Space Telescope and the Mars Science Laboratory -- that prevented other high priority missions from being started such as an Europa orbiter.

This time, the planetary Decadal Survey has a major focus on defining and costing missions. The approach is to do "Rapid Mission Architecture" studies on a large number of missions to get an idea of the engineering requirements and technical readiness. Then a smaller set of missions judged to be high priority will get full mission studies that are intended to flesh out the details of implementation. Then a small number of missions will receive detailed cost estimates. As I understand the process, to be proposed as a priority mission, a mission has to make it through all three stages, and not all missions that get through the costing stage will make the shorter list of recommended missions. Only a minority of proposed missions will make the cut at each level of assessment and progress to the next stage.

Three organizations -- NASA Goddard, John Hopkin's APL, and NASA's JPL -- will perform the rapid architectures and full mission studies. Then an outside firm will prepare the cost estimates.

The majority of missions that will enter the process will be proposed by the community itself through the hundreds of White Papers and many panel meetings. To kick start the process, however, the panels and steering committee selected several missions prior to the delivery of the White Papers. Early assessment doesn't mean anything in terms of priority. The goal was to even out the work flow for the organizations involved by getting a head start.

Steve Squyres, chair of the process, listed the first wave of missions in a letter to the community. You can read the full letter at http://www.lpi.usra.edu/decadal/vexag/newsletters/100309.pdf. The rest of this blog entry quotes the sections that list the first wave of missions to assessed. As an editorial note, I'll point out how wide ranging the types of missions are. A wide net appears to be being cast to find the intersection of the best science return and the best mission readiness and cost effectiveness.

"Prior to receiving the white papers, each panel met to identify a first set of candidate missions for study. Mission candidate studies were then reviewed and approved by the steering group, and an organization (APL, Goddard, or JPL) was chosen to conduct each study. These studies are just getting underway. IT IS IMPORTANT TO NOTE THAT THESE ARE JUST THE FIRST SET OF MISSION CANDIDATE STUDIES, selected before the white papers were received. There will be many more that have been motivated by the white papers once the white papers have been assessed.

"Six of the studies are of the type known as “Rapid Mission Architecture” studies. These are high-level studies of overall mission architecture that we expect to take a few weeks. The purpose of these studies is to explore the trade space for a mission candidate, and identify a “point design” for possible subsequent study in much greater depth.

"The six Rapid Mission Architecture studies are:

Mercury lander mission (APL)

Venus near-surface mobile explorer mission (Goddard)

Mars 2018 skycrane capabilities study (JPL)

Uranus system mission (APL)

Neptune/Triton mission (JPL)

Enceladus flyby/sample return mission (JPL)

"There are also two full mission studies. These will be more time-consuming and labor-intensive, and are intended to take these mission concepts to the point where they are ready for a full independent cost estimate. The two full mission studies are:

Mars trace gas orbiter mission (Goddard)

Titan lake mission (JPL)

"There is also one small study to be conducted by JPL that doesn't fit any of the above categories; this study will identify possible targets for Near Earth Object missions.

"In addition to the eight studies listed above, two mission concept studies have been identified that have already been done to a level of maturity such that an independent cost estimate should be possible. Independent cost estimates for each of those will be performed as soon as the company performing the cost estimates is under contract. Those two mission concepts are:

Mars trace gas orbiter mission studied to date by JPL

Comet surface sample return mission studied to date by APL.

"Note that undergoing an independent cost estimate is a necessary but not sufficient condition for a mission candidate to be included in the final SolarSystem2012 plan. Again, I stress that most of the studies will be commissioned once the white papers have been assessed! "

About Me

You can contact me at futureplanets1@gmail.com with any questions or comments.
I have followed planetary exploration since I opened my newspaper in 1976 and saw the first photo from the surface of Mars. The challenges of conceiving and designing planetary missions has always fascinated me. I don't have any formal tie to NASA or planetary exploration (although I use data from NASA's Earth science missions in my professional work as an ecologist).
Corrections and additions always welcome.